1. Field
The presently disclosed subject matter relates to an LED lighting unit and a vehicle lamp using the same, and more particularly to an LED lighting unit using a light guide that conforms to a light distribution standard for a vehicle lamp, and a thin vehicle lamp such as a headlight, auxiliary headlight, spot light, tail light, signal lamp, traffic lamp, or other vehicle lamp using the same.
2. Description of the Related Art
A conventional LED lighting unit mounted in vehicle lamps includes a plurality of LEDs and a reflector in general. Each of the plurality of LEDs has an optical axis located in a direction towards or corresponding with a light-emission direction of the associated vehicle lamp and reflector. Therefore, the conventional LED lighting unit illuminates both a direct light emitted by the plurality of LEDs and an indirect light reflected on the reflector forward in a direction towards or corresponding with the light-emission direction via a front lens located in front of the plurality of LEDs.
In this case, because each of the plurality of LEDs possesses characteristics of an approximately point light source, both direct light emitted from the plurality of LEDs and indirect light reflected from the reflector form a light distribution so as to scatter each projection image of a plurality of point light sources on the front lens and therefore resulting in an irregularity of brightness.
One method for resolving the above-described problem is using a flat panel display with a uniform light distribution, which is used as a surface light source. FIG. 10 is a cross-section view showing a conventional flat panel display using a plurality of LEDs. The conventional flat display is composed of a plurality of LEDs 54 and a light guide 50 which includes one surface having many diffusing dots 53 thereon in a manner so as to increase sequentially in its density from one end surface 51 of the light guide 50 towards the other end surface 52 opposite to the one end surface 51. The plurality of LEDs 54 are located in a disperse manner along the one end surface 51, of which side is low in its density.
A light emitted from the plurality of LEDs 54 enters the light guide 50 from the one end surface 51 of the light guide 50 and diffuses on the diffusing dots 53 as the light is guided in the light guide 50. The above diffusing light is further guided in the light guide 50 and illuminates from an outgoing surface 55 to the outside. For example, the conventional art is disclosed in the following patent document No. 1:                1. Patent document No. 1: Japanese Patent Application Laid Open JP2004-363059        
The flat panel display having the above-described structure can form a uniform light distribution. However, it is difficult for the flat panel display to conform to a light distribution standard for a vehicle lamp and/or to function as an LED lighting unit that is mounted in a vehicle lamp. Specifically, the flat panel display has two characteristics that make it difficult to conform to a light distribution standard for vehicle lights. One is a light distribution characteristic in which a vicinity at which a horizontal line and a vertical line cross in a light distribution pattern is the brightest point and the brightness at measuring points spaced away from the crossing point gradually decreases as the distance from the crossing point increases. The other characteristic is a brightness characteristic that makes it difficult to meet brightness requirements or standard at each of the measuring points.
The above-described problem may be technically resolved by increasing the number of LEDs. However, because the number of LEDs is limited to a size of a light guide that is limited to a size of a vehicle lamp, the above-described problem may not be practically resolved.
The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, an embodiment of the disclosed subject matter can include an LED lighting unit using a light guide that conforms to a light distribution standard for a vehicle lamp, and can include a thin vehicle lamp using the LED lighting unit with a favorable light distribution pattern. In addition, when the LED lighting unit is used as a flat panel display such as a back light unit and the like in a personal computer, a vending machine, etc., it can also be used as a lighting unit for illuminating a front of its display unit along with a flat panel display.